The present invention relates generally to data communications processes that enable high processing gains to be realized in systems requiring diversity transmissions. More specifically, the invention relates to a system and method of simplified interleaving for turbo coded or concatenated coded systems in which only a single interleaver is required and is used in an iterative manner in order to create diversity transmissions.
Conventionally, data communications systems, either voice or non-voice, make use of signal diversity or redundancy when transmitting information to provide an improvement in performance without compromising certain other aspects of the data transmissions system. Two conventional techniques which are used that add diversity are known as interleaving and forward-error correcting (FEC) coding.
Interleaving requires that an input data sequence is permuted or reordered into another sequence. For example a series of numbers (1, 2, 3, 4, 5, 6, 7, 8, 9, 0) may be reordered via a mathematical transformation into a different order (6, 5, 4, 1, 2, 0, 3, 8, 7, 9). The interleaving operation transposes the original position of each symbol in a finite input sequence to a new position by operation of the interleaver. This reordering process is called interleaving and may be performed in a number of ways.
When the signal is received at the transmission destination, the signal is again reordered, putting the data sequence back into the original order. This process is called de-interleaving and it is the inverse of the interleaving process.
Conventionally, FEC coding techniques are also used in the transmission process. Some of the best performing coding processes are turbo-codes. Conventionally a variety of turbo-code interleaver designs exist that require less complexity when decoding. Three of the most popular interleaver designs are 1) rectangular interleavers; 2) pseudo-random interleavers; and 3) S-random interleavers. Out of these the S-random interleavers are often seen to be better performing than the others. The S-random interleavers exploit the property of not mapping neighbor positions within a certain sequence length, to neighbor positions exhibiting the same length. The problem with using a S-random interleaver is that computing the address permutation in realtime is difficult and thus can limit the data rates when using this type of interleaver. Alternatively, the address permutation can be pre-computed and stored in memory to avoid realtime computations. However, this can require large memory storage for the highest performance turbo coded systems, because the turbo code performance is greatest when using large interleavers.
One turbo-code like FEC system is serially-concatenated convolutional coding and modulation with memory, such as continuous-phase modulation or differentially-encoded modulation. An interleaver is placed between the encoder and the modulator. This system is completely analogous to serially-concatenated convolutional codes, except that the inner code is replaced with the memory inherent in the modulation. As is conventionally done with turbo-like coding schemes, the receiver iterates between the inner decoder or demodulator and the outer decoder.
In conjunction with interleaving and FEC coding, repeat transmissions are often used to add time and frequency diversity to the data sequence.
Demodulation and decoding is typically performed by combining repeat transmissions and performing de-interleaving and FEC decoding.
Because of the computational complexity or large memory requirements, it may not be desirable to utilize multiple interleavers or large interleavers for implementing diversity transmission. Accordingly, there is a need for a system and method in which a single interleaver may be iteratively used to provide diversity transmissions.
It would be desirable to provide a system and/or method that provides one or more of these or other advantageous features. Other features and advantages will be made apparent from the present specification. The teachings disclosed extend to those embodiments which fall within the scope of the appended claims, regardless of whether they accomplish one or more of the aforementioned needs.